寫開(kāi)源項(xiàng)目的時(shí)候需要做seek功能，使用了av_seek_frame的功能，記錄如下。先看段文檔

int av_seek_frame   (   AVFormatContext * s,

int stream_index,

int64_t timestamp,

int flags

)

Seek to the keyframe at timestamp.

'timestamp' in 'stream_index'.

Parameters

s   media file handle

stream_index    If stream_index is (-1), a default stream is selected, and timestamp is automatically converted from AV_TIME_BASE units to the stream specific time_base.

timestamp   Timestamp in AVStream.time_base units or, if no stream is specified, in AV_TIME_BASE units.

flags   flags which select direction and seeking mode

#define AVSEEK_FLAG_BACKWARD 1 ///< seek backward

#define AVSEEK_FLAG_BYTE    2 ///< seeking based on position in bytes

#define AVSEEK_FLAG_ANY      4 ///< seek to any frame, even non-keyframes

#define AVSEEK_FLAG_FRAME    8 ///< seeking based on frame number

Returns

>= 0 on success

解釋###

timebase指的是時(shí)間戳，對(duì)應(yīng)pts時(shí)間戳，如果index是-1，則使用AV_TIMEBASE作為timebase并由ffmpeg自動(dòng)轉(zhuǎn)換成默認(rèn)時(shí)間戳， 如果指定了stream那么就要使用相應(yīng)的stream的timebase來(lái)計(jì)算pts了。這里注意的是比如seek到32s不能簡(jiǎn)單的直接32*AV_TIMEBASE來(lái)計(jì)算時(shí)間戳，因?yàn)閜ts不一定是從0開(kāi)始的，所以要加上起始的pts。

stream_index是選擇針對(duì)哪一條媒體流來(lái)做seek

flag用來(lái)指定尋找尋找的I幀和指定點(diǎn)之間的位置關(guān)系，因?yàn)閟eek過(guò)去的時(shí)間點(diǎn)不一定就處在I幀的地方，解碼需要依賴于I幀，所以這時(shí)候就得選擇一個(gè)附近的I幀，flag表明要seek到當(dāng)前幀的前面一個(gè)I幀還是后面一個(gè)I幀

seek到32s的例子###

int ret = av_seek_frame(inputFormatContext, -1, ((double)ms/(double)1000)*AV_TIME_BASE + (double)inputFormatContext->start_time, AVSEEK_FLAG_BACKWARD);//不指定stream進(jìn)行seek

int ret = av_seek_frame(inputFormatContext, videoIndex, (double)videoTimeBase.den/(double)videoTimeBase.num * ((double)ms/(double)1000)*AV_TIME_BASE + (double)inputFormatContext->start_time/(double)AV_TIME_BASE*((double)videoTimeBase.den/(double)videoTimeBase.num)*/, AVSEEK_FLAG_BACKWARD);//指定stream進(jìn)行seek